Thermal circuit-protector.



PATENTED NOV.-17, 1903.

0. c. HOPFMANN. I THERMAL CIRCUIT PROTECTOR.

APPLICATION FILED JAN. 19, 1903.

N0 MODEL.

own; uns (:0 o. wAsHwaTrw o c UNITED STATES Patented November 1'7, 1903.

PATENT OEETQE.

OTTO C. HOFFMANN, OF CHICAGO, ILLINOIS, ASSIGNOR TO FREDRIC GREER, OFCHICAGO, ILLINOIS.

THERMAL CIRCUIT-PROTECTOR.

SPECIFICATION forming part of Letters Patent No. 744,197, dated November17, 1908.

Application filed January 19, 1903. Serial No. 139,590. (No model.)

To all whom it may concern.-

Be it known that I, Orro O. HOFFMANN, a citizen of the United States,residing at Chicago, in the county of Cook and State of Illinois, haveinvented certain new and useful Improvements in ThermalCircuit-Protectors, of which the following is a specification.

One of the objects of this invention is the production of acircuit-protector having a fusible connection for permitting the openingof the protected circuit, also having means for automatically restoringthe fusible connection, so that the protector may be used an indefinitenumber of times without repairs.

A furtherobject of the invention is the embodiment of such an instrumentin compact and simple form.

In the accompanying drawings, Figure 1 is longitudinal central sectionthrough a circuitprotector embodying the features of my invention. Fig.2 is a perspective view of the circuit-protector. Fig. 3 is a transversesection on dotted line 3 3 of Fig. 1. Fig. 4 is a perspective View ofthe spring-fingers held normally in contact with relatively stationaryears by means of the melting of a film of solder connecting the fingerswith the ears. Fig. 5 is a longitudinal central section through acircuit-protector, illustrating a modified form of my invention. Fig. 6illustrates the cireuit-protectorin operative relation with circuitconnections.

In the embodiment herein shown of my invention I provide a cylindricalbody portion 1, formed of insulating material, and mount on said bodyportion the two end pieces 2 and 3, which end pieces are secured to saidbody portion by means of the pins 4. The end piece 2 is provided with aneck 5 and flanged head 6, while the end piece 3 has two cars 7, with anopening 8 between said ears. Within the body portion 1 and extendingaxially thereof is a small graphite pencil 9, bearing at one end againstthe U-shaped spring 10 and at its other end seated in a socket-piece 11.The socket-piece 11 has an annular base 12 and an integral stud 13projecting from the rear side of said disk. Two integral springfingers14, united by a base portion 15, lie between and contact the two ears 7,being socured to the base portion 12 or" the socketpiece by means ofsaid stud 13, which passes through a suitable opening in the baseportion 15 of said spring-fingers and is riveted down upon said baseportion. The spring-fingers 14: are formed with diverging outer ends 16,and said fingers are held rigidly in contact with the ears 7 by means offilms 17 of solder having a low melting-point. The spring-fingers 14 areprovided at their upper and lower edges with outwardly-extending flanges18, the purpose of which flanges is to keep the solder films 17 coveredin order to prevent the escape of the solder when that metal is melted.

The protector herein illustrated is intended to be used between twosprings 19 and 20, provided with slots 21 and 22, respectively, at theirupperends for receiving the neck 5 of the end piece 2 and the outer endsof the spring-fingers 14:. These springs have a tendency to separate,the spring being adapted to contact the ground connection 23, but heldfrom contact therewith by the spring-fingers 14:. The springs 19 and 20form a portion of the circuit in which the instrument to be protected isplaced, which circuit is completed by mounting the protector between thefree ends of said springs, as shown in Figs. 1 and 6. The circuitthrough said protector, beginning at the spring 19, comprises the endpiece 2, the U-shaped spring 10, the graphite pencil 9, the socket-piece11, and the end piece 3, including the ears 7, the solder films 17, andthe spring-fingers 14.

In the normal use of the protector the usual current passes through thecircuit of said protector from the spring 19 to the spring 20. When acurrent of a high intensity trespasses upon the circuit, it generates aconsiderable amount of heat in passing through the graphite pencil9,which heat is transmitted through the socket-piece 11, the ears 7, andthe springfingers 1a to the solder films 17, melting said solder andpermitting the spring-fingers 1:1: to be separated from the ears 7 bythe stripping action of the spring 20 in slipping over the divergingends 16 of said spring-fingers, thus mechanically breaking the circuit.The

spring 20 immediately contacts the ground connection 23, grounding oneside of the current, and the spring-lingers let by reason of theirelasticity return to the ears 7, embed ICQ ding themselves in the stillwarm solder of the films 17. Inasmuch as the circuit is now open, theheat subsides and the solder films cool, firmly reuniting thespring-fingers 14; with the ears 7. The circuit is reestablished byflexing the spring into the position shown in Fig. 1 and slipping thespring-fingers 14; into the slotted opening 22 of said spring 2 In themodified form illustrated in Fig. 5 a coil 9, of fine German-silverwire, surrounding the ears 7, is substituted for the graphite pencil 9.This wire is of high resistance and is heated when a current of anyconsiderable intensity passes over the circuit of the proteetor. Theapplication and action of this modified form of protector are the sameas hereinbefore described.

It is apparent that various changes might be made in the constructionsherein shown and described without departing from the spirit and scopeof my invention, wherefore I desire to have it understood that I do notlimit myself to the precise details herein set forth.

I claim as my invention- 1. In a thermal circuit-protector, incombination, a fixed member; a spring; a springfinger fixed withrelation to said fixed member and tending to lie in contact therewith,which finger is adapted to hold said spring flexed, said spring tendingto separate the spring-finger from said fixed member; and a solderconnection between said fixed member and said spring-finger.

2. In a thermal circuit-protector, in combination, a fixed member; aspring; a springfinger fixed with relation to said fixed member andtending to lie in contact therewith, which finger is adapted to holdsaid spring flexed, said sprin tending to separate the spring-fingerfrom said fixed member; a solder connection between said fixed memberand said spring-finger; and a substance offering comparatively highresistance to the passage of an electric current, in proximity to saidsolder connection.

3. In a thermal circuit-protector, in combination, two cars; aspring-finger adapted to lie in contact with each one of said cars; aspring adapted to be held flexed by said springfingers and tending toseparate said springfingers from said ears; and a fusible solderconnection between each one of said ears and its spring-finger.

4. In a thermal circuit-protector, in combination, two ears; a spring; aspring-finger adapted to lie in contact with each one of said ears andto hold said spring flexed, said spring tending to separate thespring-fingers from said ears; and a fusible solder connection betweeneach of said ears and its spring-finger.

5. In a thermal circuit-protector, in combination, two ears; a spring; aspring-finger adapted to lie in contact with each one of said ears andto hold said spring flexed, said spring tending to separate thespring-fingers from said ears; afusible solderconnection between each ofsaid ears and its spring-finger; and a substance offering comparativelyhigh resistance to the passage of an electric current, in proximity tosaid solder connection.

6. In a thermal circuit-protector, in combination, a fixed member; aspring; a springfinger fixed with relation to said fixed member andtending to lie in contact therewith, which finger has a projectionadapted to engage said spring to hold the latter flexed, said projectionalso causing said spring to tendto separate said spring-finger from saidfixed member; and a fusible solder connection between said fixed memberand said spring-finger.

7. In a thermal circuit-protector, in combination, a fixed member; aspring; a springfinger fixed with relation to said fixed member andtending to lie in contact therewith, which finger has a projectionadapted to engage said spring to hold the latter ficxed, said projectionalso causing said spring to tend to separate said spring-finger fromsaid fixed member; a fusible solder connection between said fixedmemberand said spring-finger; and a substance offering comparativelyhigh resistance to the passage of an electric current in proximity tosaid solder connection.

8. In a thermal circuit-protector, in combination, two ears; a pair ofspring-fingers having inclined outer ends, said fingers adapted to liebetween said ears, each of said fingers contacting one of the ears;-afusible solder connection between each one of said ears and itsspring-finger; and a spring having an opening adapted to receive theouter ends of said spring-fingers, said spring being held flexed by saidfingers when the fingers are held by said solder connection but tendingto separate said fingers from said ears.

9. In a ihermal circuit-protector, in combi nation, two ears; a pair ofspring-fingers having inclined outer ends, said fingers adapted to liebetween said ears, each of said fingers contacting one of the cars; afusible solder connection between each one of said ears and itsspring-finger; a spring having an opening adapted to receive the outerends of said spring-fingers, said spring being held fiexed by saidfingers when the fingers are held by said solder connection but tendingto separate said fingers from said ears; and a graphite pencil in anelectric circuit, in proximity to said solder connection.

10. In a thermal circuit-protector, in combination, a cylindrical bodyportion; a socketpiece therein; a graphite pencil in said socket-piece;two ears fixed with relation to said body portion; two spring-fingershaving inclined projections, fixed with relation to said socket-pieceand adapted to lie in contact with said ears; and a spring adapted to beengaged by said projections and to be held flexed by said spring-fingerswhen said fingers are held by said solder connection in contact withsaid ears.

IIO

11. In a thermal circuit-protector, in combination, a body portion; twoend pieces insulated from said body portion; a graphite pencil Withinsaid body portion; a socketpiece for said pencil, in electric connectionwith one of said end pieces; a spring for electrically connecting thegraphite pencil with the other one of said end pieces; two ears on oneof said end pieces; a pair of spring-fingers secured to saidsocket-piece, said springfingers having inclined outer ends and adaptedto contact said cars; a fusible solder connection between said ears andsaid springfingers; and a spring adapted to engage the inclined ends ofsaid spring-fingers and to be held flexed by said fingers when saidfingers

